Storage tanks used for the underground bulk storing of liquids are predominantly formed either from sheet metal or from fibrous reinforced resinous material. Such tanks typically hold up to about 50,000 gallons of liquid. The tanks must be sufficiently strong to withstand internal forces exerted by the weight of the liquid as well as normal external ground forces.
Underground storage ranks made from sheet metal have a cylindrical-shaped main body with flattened ends welded thereto. The thickness or gauge of sheet metal used will depend on the size of the tank, the greater the size the greater the requisite sheet metal thickness. It follows that the larger sized tanks are more expensive to build primarily because of increased raw material costs.
There are also presently used storage tanks made from fibrous reinforced resinous materials. These tanks as well are expensive to build, though primarily because of the labor intensive steps which are needed. The larger tanks, e.g. those having a capacity greater than about 500 gallons are ribbed. That is, a series of ribs extend around a cylindrical-shaped main body. The ribs are either added to the exterior of a pre-formed cylindrical-shaped main body or are formed simultaneously with the main body utilizing a removable mold. In either case, the ribs strengthen the tank.
Underground storage tanks made from metal or fibrous reinforced resinous material directly compete in the same market. Each type of tank has its advantages. However, each type of tank has one common disadvantage, i.e. each is expensive to build.
In accord with a need, there has been developed a new underground storage tank. The tank enjoys many of the benefits of known metal tanks, but is less expensive to build.